Surgical head clamps or skull clamps generally are provided with two types of mechanisms to hold the head in position. One type of clamps uses pads that are forced against the patient's head to hold the head in position. Examples of head clamps of this type are disclosed in U.S. Pat. Nos. 4,108,426 and 4,545,572.
A second type of head clamp uses a series of head engaging pins which engage the patient's skull at three points and provide positive anchorage of the head engaging pins into the skull. If the head engaging pins are held in a stable position, there is little likelihood that the skull will move relative to the head engaging pins during the surgical procedure.
The head clamp disclosed in U.S. Pat. No. 2,966,383 shows a three pin arrangement with the head engaging pins carried on hinged arms.
U.S. Pat. No. 3,099,441 discloses a surgical head clamp which contains two head engaging pins on a bracket supported by an arm and a third head engaging pin supported by another arm in the device. The two arms are brought together to adjust the space between the head engaging pins to fit the dimensions of the patient's head.
U.S. Pat. No. 3,835,861 discloses a surgical head clamp having three head engaging pins with two of the pins on a bracket and a third pin on a moveable pin carrier in which the moveable pin is held on a threaded pin carrier so finer adjustments in the relationship of the head engaging pins to the patient can be made.
U.S. Pat. No. 4,169,478 also discloses a surgical head clamp with three head engaging pins which is similar to that shown in U.S. Pat. No. 3,835,861. The head clamp includes a mechanism to rotate the bracket containing the two pins and reposition the head of the patient without releasing the head engaging pins from the patient's skull. The mechanism disclosed in U.S. Pat. No. 4,169,478 to prevent rotation employs interlocking teeth on stop members which are forced into engagement by ball actuators. The ball actuators move from dished sockets in the unlocked position to the lands between the dished sockets in the locket position. Upon repeated use and upon repeated sterilization, there is a tendency for foreign particles and debris to accumulate in the dished sockets or on the lands which prevent the positive locking of the bracket.
Although the surgical head clamp disclosed in U.S. Pat. No. 4,169,478 does offer certain advantages to the physicians, the problem exists in that the bracket can be inadvertently turned which may cause the head to move in the bracket and could cause injury to the patient. The weight of the patient in certain operating positions could exert a force against the bracket which might cause the bracket to turn if the ball actuators are not firmly positioned on the lands on the actuator disk.
The copending application Ser. No. 921,867, filed Jul. 28, 1992, discloses a head clamp which employs index pins between a rotatable bracket and the frame of the head clamp to prevent inadvertent rotation of the bracket. However, the bracket cannot be adjusted when the head engaging pins are engaging the patient's head. The patient's head must be disengaged from the pins before the bracket can be rotated.